It sounds very strange. Dont they carry radios? Its possible they were outnumbered and were running and ran out of ammo but stayed together. If they didnt have radios. Hard for me to believe someone could sneak up on them, overpower them like in a running fight but not sneak up on them. And that would take alot of people to do.
As for looting them, well maybe the people have learned from Falluja and were afraid to desecrate the bodies of four service men fearing the retaliation. If your going to loot someone, why move them into a building or enclosure?
Murder seems possible but so remotely unlikely. Hard to imagine.